Fix script gen clean up failure (#1252)

## Summary
Getting the following error when running any script
```
[DEBUG] 2023/07/05 21:06:23 go.jetpack.io/devbox/internal/shellgen/scripts.go:73: failed to clean up script file build.sh, error = remove ~/devbox/.devbox/gen/scripts/build.sh.sh: no such file or directory
```

It looks like `.sh` is wrongly appended to the existing files under the
scripts directory. This PR fixes that.

## How was it tested?
devbox run build

Author: LucilleH

internal/shellgen/scripts.go

@@ -54,21 +54,22 @@ func WriteScriptsToFiles(devbox devboxer) error {
 	if err != nil {
 		return errors.WithStack(err)
 	}
-	written[ScriptPath(devbox.ProjectDir(), HooksFilename)] = struct{}{}
+	written[HooksFilename] = struct{}{}
 
 	// Write scripts to files.
 	for name, body := range devbox.Config().Scripts() {
 		err = WriteScriptFile(devbox, name, ScriptBody(devbox, body.String()))
 		if err != nil {
 			return errors.WithStack(err)
 		}
-		written[ScriptPath(devbox.ProjectDir(), name)] = struct{}{}
+		written[name] = struct{}{}
 	}
 
 	// Delete any files that weren't written just now.
 	for _, entry := range entries {
-		if _, ok := written[entry.Name()]; !ok && !entry.IsDir() {
-			err := os.Remove(ScriptPath(devbox.ProjectDir(), entry.Name()))
+		scriptName := strings.TrimSuffix(entry.Name(), ".sh")
+		if _, ok := written[scriptName]; !ok && !entry.IsDir() {
+			err := os.Remove(ScriptPath(devbox.ProjectDir(), scriptName))
 			if err != nil {
 				debug.Log("failed to clean up script file %s, error = %s", entry.Name(), err) // no need to fail run
 			}